The present invention relates generally to integrated circuit (IC) designs, and more particularly to a word line voltage control circuit for memory devices.
Performance requirements for microprocessors, portable devices, and wireless devices have increased significantly over the last few decades. Device sizes have been shrinking continuously in order to meet the heightened performance requirements. As a result, a large number of logic circuits and memory cells are packed in a relatively small memory chip. Low power design becomes very important for the memory chip to reduce power consumption and remain thermally stable.
Various circuits and methods have been developed to reduce current leakage for memory devices, such as static random access memory (SRAM) and dynamic random access memory (DRAM), during a stand-by or sleep mode. One method uses a well bias to reduce sub-threshold leakage in a standby mode. In another method, a lower supply voltage is used to reduce junction leakage, sub-threshold leakage and gate leakage. In yet another method, the voltage at a power supply node of a memory device is reduced to the lowest possible level during a sleep mode, such that the data can be retained in memory cells, while the peripheral logic circuits are completely turned off. This is typically called a full-sleep-mode design.
In a full-sleep-mode design, the power consumption of the sleep mode is reduced below than that of the standby mode. In some cases, the power consumption of the sleep mode can be reduced to below one tenth of the standby mode power consumption. It is anticipated that the full-sleep-mode design will become more popular in reducing power consumption of memory devices.
Conventionally, the full-sleep-mode design requires an additional AC (alternating current) voltage control circuit connected to word lines of a memory device. In the normal operation mode, a decoder is enabled to control the word lines, while the AC voltage control circuit is disabled. In the sleep mode, the decoder is disabled and the AC voltage control circuit generates a signal to pull the word lines to either ground voltage or VSS.
Since the conventional voltage control circuit is connected to AC power, it is complex in design. Accordingly, there is a need for a word line voltage control circuit that can achieve the functions of the AC voltage control circuit while being simpler in design.